The most common solution to prevent galvanic corrosion is to select metals that are close in the electrochemical sequence. Separating incompatible metals reduces the risk of these cells deteriorating. Depending on the extent of galvanic corrosion, stainless steel in contact with materials such as copper is less at risk than when in contact with aluminum.
While aluminum can react negatively to stainless steel, large areas of aluminum in contact with stainless steel are acceptable depending on local environmental conditions. Severe corrosion can occur in marine environments. However, there are methods that can be used to reduce this effect. A good way to reduce corrosion is to use an isolating coating or paint on the aluminum and steel to electrically isolate them. Insulating washers are also effective in isolating the two different materials and creating a relatively safe surface area.
In addition to corrosion, stainless steel may also discolor when combined with aluminum. This is also known as "tea staining." Discoloration can be prevented by using insulation and regular maintenance. Passivation can also be used to form a passive film on fasteners to improve corrosion resistance.
As a leading stainless steel fastener expert and working with a full range of stainless steel and aluminum product manufacturers and suppliers across a variety of industries, we can help you ensure that you are using the best products with the highest corrosion protection performance.
Customers often ask if it is possible or recommended to use stainless steel fasteners with aluminum. It is well known that two metals in contact can cause corrosion. Corrosion occurs when two dissimilar materials are combined in a corrosive electrolyte. This can occur when certain materials, such as aluminum, come in contact with stainless steel. However, there are ways to use stainless steel and aluminum together while preventing corrosion.
The most common solution to preventing electrochemical corrosion is to choose metals that are close in the electrochemical series. Keeping incompatible metals separate can reduce the risk of these cells deteriorating. Depending on the extent of electrochemical corrosion, stainless steel in contact with materials such as copper is less at risk than when it is in contact with aluminum.
Reactions of Steel and Aluminum
While aluminum can react negatively to stainless steel, large areas of aluminum in contact with stainless steel can be acceptable depending on local environmental conditions. An example of a safe use of stainless steel fasteners with aluminum is using stainless steel bolts to fasten aluminum road guardrails. In this case, the surface area of the aluminum is very large relative to the surface area of the stainless steel bolts, so the risk of severe corrosion is very low.
Severe corrosion can occur in marine environments. However, there are methods that can be used to reduce this effect. A good way to reduce corrosion is to use an insulating coating or paint on the aluminum and steel to electrically isolate them. Insulating washers can also effectively isolate the two dissimilar materials and create a relatively safe surface area.
How to Tell the Difference Between Aluminum and Stainless Steel
Not sure what material you're dealing with? You can usually tell the difference between aluminum and stainless steel visually, as the former has a duller appearance. Aluminum is also much lighter and softer than steel. However, this isn't always obvious; it depends on the alloys involved. Different manufacturing processes can produce different looks and finishes.
One way to be sure is to use the key test. Take a key and drag it along a flat surface. If the surface is aluminum, it will scratch deeply without much pressure, as aluminum is much softer than steel. Steel won't scratch at all or will only scratch the surface.
What to Put Between Steel and Aluminum
When using stainless steel fasteners with aluminum surfaces, you can prevent corrosion by putting something between the two metals. Plastic or rubber washers or spacers are good suggestions.
In addition to corrosion, stainless steel may also discolor when combined with aluminum. This is also known as "tea staining." Discoloration can be prevented by using insulating materials and regular maintenance. Passivation can also be used to create a passive film on the fastener to improve corrosion resistance.
How to Fasten Aluminum to Steel
While it is relatively safe to use stainless steel fasteners on large aluminum surfaces, the reverse is not true. If you use aluminum rivets or other fasteners to connect large steel pieces, corrosion will set in and break down the fasteners, eventually causing the parts to come loose.